The joking caricature - "I'm a scientist, I don't believe in anything" - almost fits me. Almost, but I'm not a scientist. The rest is pretty close. I like the notion that the way to respond to evidence and theories is not to ask "can I believe in this", but to ask "must I believe in this". The answer is very, very seldom yes, you must believe.

So I try, not always convincingly, to keep a sceptical distance from global warming belief. I do succeed in avoiding global warming hysteria since that is plainly dumb as well as mean spirited, and usually instrumental - an excuse for authoritarians to try yet again to seize control of society. So, I always welcome a new paper by Richard S. Lindzen, Alfred P. Sloan Professor of Atmospheric Sciences, Massachusetts Institute of Technology.

The issue of man induced climate change involves not the likelihood of dangerous consequences, but rather their remote possibility. The main areas of widespread agreement (namely that global mean temperature has risen rather irregularly about 0.6C over the past century, that atmospheric levels of carbon dioxide have increased about 30% over the past century, and that carbon dioxide by virtue of its infrared absorption bands should contribute to warming) do not imply dangerous warming. Indeed, we know that doubling carbon dioxide should lead to a heating of about 3.7 watts per square meter, and that man made greenhouse heating is already about 2.7 watts per square meter. Thus, we have seen less warming than would be predicted by any model showing more than about 0.8 degrees C warming for a doubling of carbon dioxide. This is consistent with independent identifications of negative feedbacks.

Alarming scenarios, on the other hand, are typically produced by models predicting 4 degrees C. After the fact, such models can only be made to simulate the observed warming by including numerous unknown factors which are chosen to cancel most of the warming to the present, while assuming that such cancellation will soon disappear.

That is the issue isn't it? We are pretty clear that "carbon dioxide by virtue of its infrared absorption bands should contribute to warming", but how much? The evidence seems to point to "not much", and so the sensible response is to tighten our belts a bit and work a bit smarter to emit less and scrub up what we already spilled. Live and learn. But we don't really know how much things will warm and would do well to investigate that with vigor. Politicians, however, see an opportunity to enlarge their remit, and so we have rampant alarmism. Caped crusaders are coming out of the woodwork offering to save the day in return for a vote or a donation.

What we need is a good alternative theory to help us look more closely at the ones we have.

A new theory to explain global warming was revealed at a meeting at the University of Leicester (UK) and is being considered for publication in the journal "Science First Hand". The controversial theory has nothing to do with burning fossil fuels and atmospheric carbon dioxide levels. According to Vladimir Shaidurov of the Russian Academy of Sciences, the apparent rise in average global temperature recorded by scientists over the last hundred years or so could be due to atmospheric changes that are not connected to human emissions of carbon dioxide from the burning of natural gas and oil. Shaidurov explained how changes in the amount of ice crystals at high altitude could damage the layer of thin, high altitude clouds found in the mesosphere that reduce the amount of warming solar radiation reaching the earth's surface.

Shaidurov has used a detailed analysis of the mean temperature change by year for the last 140 years and explains that there was a slight decrease in temperature until the early twentieth century. This flies in the face of current global warming theories that blame a rise in temperature on rising carbon dioxide emissions since the start of the industrial revolution. Shaidurov, however, suggests that the rise, which began between 1906 and 1909, could have had a very different cause, which he believes was the massive Tunguska Event, which rocked a remote part of Siberia, northwest of Lake Baikal on the 30th June 1908. . .

. . . the most potent greenhouse gas is water, explains Shaidurov and it is this compound on which his study focuses. According to Shaidurov, only small changes in the atmospheric levels of water, in the form of vapour and ice crystals can contribute to significant changes to the temperature of the earth's surface, which far outweighs the effects of carbon dioxide and other gases released by human activities. Just a rise of 1% of water vapour could raise the global average temperature of Earth's surface more then 4 degrees Celsius.

The role of water vapour in controlling our planet's temperature was hinted at almost 150 years ago by Irish scientist John Tyndall. Tyndall, who also provided an explanation as to why the sky is blue, explained the problem: "The strongest radiant heat absorber, is the most important gas controlling Earth's temperature. Without water vapour, he wrote, the Earth's surface would be 'held fast in the iron grip of frost'." Thin clouds at high altitude allow sunlight to reach the earth's surface, but reflect back radiated heat, acting as an insulating greenhouse layer.

Water vapour levels are even less within our control than CO2 levels. According to Andrew E. Dessler of the Texas A & M University writing in 'The Science and Politics of Global Climate Change', "Human activities do not control all greenhouse gases, however. The most powerful greenhouse gas in the atmosphere is water vapour, he says, "Human activities have little direct control over its atmospheric abundance, which is controlled instead by the worldwide balance between evaporation from the oceans and precipitation."

As such, Shaidurov has concluded that only an enormous natural phenomenon, such as an asteroid or comet impact or airburst, could seriously disturb atmospheric water levels, destroying persistent so-called 'silver', or noctilucent, clouds composed of ice crystals in the high altitude mesosphere (50 to 85km). The Tunguska Event was just such an event, and coincides with the period of time during which global temperatures appear to have been rising the most steadily - the twentieth century. There are many hypothetical mechanisms of how this mesosphere catastrophe might have occurred, and future research is needed to provide a definitive answer.

Trees emit methane. We just found out this year because no one ever thought to test that before. It's a good reminder to keep an open mind, to withhold belief and continue to reason from evidence, and assume that you will be shown to be wrong when you have better evidence to reason from, that you will happily debunk yourself when you learn something new.

Update:

This may explain some of the anomolies of warming.

According to this new research, ozone was responsible for one-third to half of the observed warming trend in the Arctic during winter and spring. Ozone is transported from the industrialized countries in the Northern Hemisphere to the Arctic quite efficiently during these seasons. . .

The impact of ozone air pollution on climate warming is difficult to pinpoint because, unlike other greenhouse gases such as carbon dioxide, ozone does not last long enough in the lower atmosphere to spread uniformly around the globe. Its warming impact is much more closely tied to the region it originated from. To capture this complex picture, GISS scientists used a suite of three-dimensional computer models that starts with data on ozone sources and then tracks how ozone chemically evolved and moved around the world over the past century.

The warming impact of low-altitude ozone on the Arctic is very small in the summer months because ozone from other parts of the globe does not have time to reach the region before it is destroyed by chemical reactions fueled by ample sunshine. As a result, when it is summertime in the Northern Hemisphere, ozone-induced warming is largest near the sources of ozone emissions. The computer model showed large summer warming from ozone over western North America and eastern Europe/central Asia, areas with high levels of ozone pollution during that time of year.

The new results identify an unexpected benefit of air pollution control efforts worldwide, according to lead author Drew Shindell. "We now see that reducing ozone pollution can not only improve air quality but also have the added benefit of easing climate warming, especially in the Arctic."

It seems that CO2 may be the wrong target for Arctic issues despite all the hysterical claims of politicized advocates. Continuing efforts to reduce real pollutants, those with clearly adverse health effects and those that clearly degrade local environments, makes ever more sense.

Update:

Philip points to an article about another alternative theory of climate change - not a new one but with recent support - that also comments on the problems of climate change heretics.

Veizer says high-energy rays from distant parts of space are smashing into our atmosphere in ways that make our planet go through warm and cool cycles.

Cosmic rays are hitting us all the time -- a well-known fact. What's new is that researchers are asking what cosmic rays do to our world and its weather. . .

Veizer has published his theory in Geoscience Canada, the journal of the Geological Association of Canada. The article is called Celestial Climate Driver: A Perspective from Four Billion Years of the Carbon Cycle.

In his paper, he concludes: "Empirical observations on all time scales point to celestial phenomena as the principal driver of climate, with greenhouse gases acting only as potential amplifiers."

The idea is that cosmic rays hit gas molecules in the atmosphere and form the nucleus of what becomes a water vapour droplet. These in turn form clouds, reflecting some of the sun's energy back to space and cooling the Earth.

Yet the numbers of cosmic rays vary.

When there are more cosmic rays the Earth is colder. When there are fewer cosmic rays the Earth is warmer.

"The question is, therefore, 'Where do we have lots of cosmic rays?' "

Most rays come from younger stars, which are clustered at some regions in the galaxy through which our solar system has passed its 4.5-billion-year history.

Our own sun deflects some of these rays away, but the sun's activity grows stronger and weaker. All of these factors can change the number of cosmic rays that hit us.

The Earth's magnetic field also blocks some cosmic rays. Scientists can reconstruct records of that field for the past 200,000 years, and he argues there's an extremely close match between cold times in our climate and times when the magnetic field allowed more cosmic rays to hit us.

Even in recent times he argues that other cosmic factors can affect our climate as plausibly as carbon dioxide, or more so. The warming of Earth in the past 100 years -- about 0.6 degrees Celsius -- matches a time of the sun's growing intensity, he says.

I can imagine a couterfactual history in which the popular imagination seized on cosmic rays and their variation due to the sun's cycles and the earth's magnetic field variations as well as galactic variation as we cruise through the cosmos wheeling around the galaxy, but can't settle on whether we would be fussing about cooling or warming.

But, this isn't new and doesn't add much to the investigation. What's interesting is the story of the scientist.

Questioning the fundamentals of climate change -- the theory that man-made gases such as carbon dioxide are building up and warming our climate -- is a fast way to start a nasty, personal fight in the science world.

But Veizer's credentials make it tough to challenge his findings.

The recently retired professor still holds a research chair and supervises grad students and postdoctoral fellows. A native of Bratislava, Veizer left because Russian troops entered Czechoslovakia in 1968. He's been building up honours ever since in the field of geochemistry -- learning about Earth's past by the chemistry preserved in rocks and sediments.

The Royal Society of Canada called him "one of the most creative, innovative and productive geoscientists of our times," and added: "He has generated entirely new concepts that have proven key in our understanding the geochemical history of Earth."

He won the 1992 Gottfried Wilhelm Leibniz Prize, worth $2.2 million Cdn, representing the German government's highest prize for research in any field. The prize ended up financing his research.

The judges said he "has in front of his eyes the overall picture of the Earth during its entire 4.5 billion years of evolution," and he is "one of the most creative ... geologists of his time."

Yet, for years he held back on his climate doubts. "I was scared," he says.

We are still medieval. Scientists still fear being tried for heresy. That's not news either but it is worth considering the implications: there are surely many scientists that harbor many ideas on many subjects that they neither express nor pursue because they fear professional and/or public reprisal. Academics natter on about the value of tenure in freeing them to be more open but it isn't so, tenure only protects the inadequate, not the heretic.